A 19-year-old College Park man who fatally shot two skate store employees at a Maryland mall before killing himself kept a journal indicating “some general unhappiness with his life,” police said, but authorities have yet to find a motive behind the deadly attack.

Howard County Police Chief William J. McMahon said Darion Marcus Aguilar was behind Saturday morning’s shooting at the Zumiez store on the upper level of The Mall in Columbia. But despite early and persistent reports the shooting stemmed from a romantic relationship, the chief called the reason behind the killings an “open question.”

“We have not been able to verify any type of relationship at this point between him and either of our victims,” he said.

Police late Saturday afternoon identified the store employees killed in the shooting as Brianna Benlolo, 21, of College Park and Tyler Johnson, 25, of Ellicott City. Ms. Benlolo had a 2-year-old child and was an assistant manager at the Zumiez — a store that sells skateboards, clothes and accessories.

A visibly agitated Chief McMahon reiterated at an evening news conference Sunday that police are not ruling out the possibility the shooting was domestic-related but have found nothing to make them believe that. He said the continued speculation is becoming “very frustrating for the families of our victims to continue to hear this.”

The chief said Aguilar, who lived with his mother about a half-mile from where Ms. Benlolo lived, had no adult criminal record and left no note behind to explain his actions.

Chief McMahon said officers searched Aguilar’s house late Saturday and early Sunday and took ammunition, a computer and some documents they hoped might provide insight on the shootings. Among the documents was a journal that authorities are studying for clues to the attack.

“That’s something we’re going to continue to work through tonight and in the days ahead,” Chief McMahon said.

Prince George’s County police on Sunday issued a statement saying Aguilar’s mother called them Saturday about two hours after the shooting to report her son missing. Police said an officer went to the home at about 5 p.m., talked with Aguilar’s mother and saw his journal.

“The portion of the journal that he read made him concerned for the missing person’s safety,” police said. But by that point, the shooting had already occurred.

Chief McMahon said Sunday morning that Aguilar was not immediately identified because he had “a lot of ammunition on him,” causing police to take precautions before approaching his body.

“We were concerned about whether he had booby trapped himself,” he said, adding that officials sent in a robot to examine the body and found “not very sophisticated” attempts at bombs that were made with flash powder and homemade items.

“As you know, because of those found devices that we were able to render safe, we did have concerns about, ‘Did he leave anything else in the mall?’ ” Chief McMahon said, adding that 20 K-9 teams were deployed to search the mall. “We did not find any indication of any more explosive devices.”

The weapon used in the shooting was a 12-gauge Mossburg shotgun legally purchased by Aguilar in December in Montgomery County, police said.

Chief McMahon couldn’t say whether there appeared to be any type of altercation or exchange of words before Aguilar opened fire on his victims.

Aguilar was seen on surveillance video arriving at the mall by taxi at an upstairs entrance about an hour before the shootings. Police said he was carrying a backpack and limited in his movements, going briefly downstairs and then returning upstairs to the Zumiez store before the shootings at 11:15 a.m. He fired between six and eight shots. No shots were fired by police in the course of the response.

Five other people were injured. Most were not directly related to the shooting but to the chaotic aftermath. One person who was downstairs in the food court suffered a gunshot wound to the foot. All were treated and released by Saturday night, hospital officials said.

The mall is set to reopen at 1 p.m. Monday, but people who left personal belongings behind as they rushed to get out of the area were allowed to retrieve them Sunday.

Meanwhile, a trickle of details began to emerge Sunday about the lives of Aguilar and his victims. A Montgomery County schools spokesman said Aguilar graduated from James Hubert Blake High School in Silver Spring last year.

Tydryn Scott, 19, said she was Aguilar’s lab partner in science class and described him as tall, skinny and quiet. She said he was interested in skateboarding and hung out with other skaters. She said she was stung by the news that he was the shooter.

“I’ve seen this guy in action before. Never upset, never sad, just quiet — just chill,” Ms. Scott said.

A man who answered the phone at Tyler Johnson’s residence said the family had no comment. But the victim’s aunt told a local television station that she did not believe her nephew knew Aguilar.

Ms. Benlolo’s grandfather, John Feins, said in a telephone interview from Florida that his granddaughter had a 2-year-old son and that the job at Zumiez was her first since she went back to work after her son’s birth.

“She was all excited because she was the manager there,” he said. He said his granddaughter was on good terms with her son’s father, and they shared custody.

“I mean what can you say?” he said. “You go to work and make a dollar and you got some idiot coming in and blowing people away.”